Printed circuit board with integrated temperature sensing

ABSTRACT

An extruder for a three-dimension printer uses a printed circuit board (PCB) heating element with leads having temperature-sensitive resistance. The resulting circuit can be driven at high power to heat an extruder, or at a low power with a known current to measure a resistance from which temperature can be inferred. Thus a single circuit on a printed circuit board can be driven alternately in two modes to heat and sense temperature of an extruder.

RELATED APPLICATION

This application claims the benefit of U.S. Prov. App. No. 61/680,989filed on Aug. 8, 2012, the entire content of which is herebyincorporated by reference.

BACKGROUND

There remains a need for a printed circuit board that support heatingand temperature sensing with a reduced part count.

SUMMARY

An extruder for a three-dimension printer uses a printed circuit board(PCB) heating element with leads having temperature-sensitiveresistance. The resulting circuit can be driven at high power to heat anextruder, or at a low power with a known current to measure a resistancefrom which temperature can be inferred. Thus a single circuit on aprinted circuit board can be driven alternately in two modes to heat andsense temperature of an extruder.

BRIEF DESCRIPTION OF THE FIGURES

The invention and the following detailed description of certainembodiments thereof may be understood by reference to the followingfigures:

FIG. 1 is a block diagram of a three-dimensional printer.

FIG. 2 shows a combined heater and temperature sensor integrated with aprinted circuit board.

FIG. 3 shows a method for operating a printed circuit board withintegrated temperature sensing.

FIG. 4 shows a method for fabricating conductive traces on a printedcircuit board.

FIG. 5 shows a conductive trace forming a heating element.

DETAILED DESCRIPTION

All documents mentioned herein are hereby incorporated in their entiretyby reference. References to items in the singular should be understoodto include items in the plural, and vice versa, unless explicitly statedotherwise or clear from the text. Grammatical conjunctions are intendedto express any and all disjunctive and conjunctive combinations ofconjoined clauses, sentences, words, and the like, unless otherwisestated or clear from the context. Thus the term “or” should generally beunderstood to mean “and/or” and so forth.

The following description emphasizes three-dimensional printers usingfused deposition modeling or similar techniques where a bead of materialis extruded in a layered series of two dimensional patterns as “roads,”“paths” or the like to form a three-dimensional object from a digitalmodel. It will be understood, however, that numerous additivefabrication techniques are known in the art including without limitationmultijet printing, stereolithography, Digital Light Processor (“DLP”)three-dimensional printing, selective laser sintering, and so forth.Such techniques may benefit from the systems and methods describedbelow, and all such printing technologies are intended to fall withinthe scope of this disclosure, and within the scope of terms such as“printer”, “three-dimensional printer”, “fabrication system”, and soforth, unless a more specific meaning is explicitly provided orotherwise clear from the context.

FIG. 1 is a block diagram of a three-dimensional printer. In general,the printer 100 may include a build platform 102, an extruder 106, anx-y-z positioning assembly 108, and a controller 110 that cooperate tofabricate an object 112 within a working volume 114 of the printer 100.

The build platform 102 may include a surface 116 that is rigid andsubstantially planar. The surface 116 may provide a fixed, dimensionallyand positionally stable platform on which to build the object 112. Thebuild platform 102 may include a thermal element 130 that controls thetemperature of the build platform 102 through one or more active devices132, such as resistive elements that convert electrical current intoheat, Peltier effect devices that can create a heating or coolingaffect, or any other thermoelectric heating and/or cooling devices. Thethermal element 130 may be coupled in a communicating relationship withthe controller 110 in order for the controller 110 to controllablyimpart heat to or remove heat from the surface 116 of the build platform102.

The extruder 106 may include a chamber 122 in an interior thereof toreceive a build material. The build material may, for example, includeacrylonitrile butadiene styrene (“ABS”), high-density polyethylene(“HDPL”), polylactic acid (“PLA”), or any other suitable plastic,thermoplastic, or other material that can usefully be extruded to form athree-dimensional object. The extruder 106 may include an extrusion tip124 or other opening that includes an exit port with a circular, oval,slotted or other cross-sectional profile that extrudes build material ina desired cross-sectional shape.

The extruder 106 may include a heater 126 (also referred to as a heatingelement) to melt thermoplastic or other meltable build materials withinthe chamber 122 for extrusion through an extrusion tip 124 in liquidform. While illustrated in block form, it will be understood that theheater 126 may include, e.g., coils of resistive wire wrapped about theextruder 106, one or more heating blocks with resistive elements to heatthe extruder 106 with applied current, an inductive heater, or any otherarrangement of heating elements suitable for creating heat within thechamber 122 sufficient to melt the build material for extrusion. Theextruder 106 may also or instead include a motor 128 or the like to pushthe build material into the chamber 122 and/or through the extrusion tip124.

In general operation (and by way of example rather than limitation), abuild material such as ABS plastic in filament form may be fed into thechamber 122 from a spool or the like by the motor 128, melted by theheater 126, and extruded from the extrusion tip 124. By controlling arate of the motor 128, the temperature of the heater 126, and/or otherprocess parameters, the build material may be extruded at a controlledvolumetric rate. It will be understood that a variety of techniques mayalso or instead be employed to deliver build material at a controlledvolumetric rate, which may depend upon the type of build material, thevolumetric rate desired, and any other factors. All such techniques thatmight be suitably adapted to delivery of build material for fabricationof a three-dimensional object are intended to fall within the scope ofthis disclosure.

The x-y-z positioning assembly 108 may generally be adapted tothree-dimensionally position the extruder 106 and the extrusion tip 124within the working volume 114. Thus by controlling the volumetric rateof delivery for the build material and the x, y, z position of theextrusion tip 124, the object 112 may be fabricated in three dimensionsby depositing successive layers of material in two-dimensional patternsderived, for example, from cross-sections of a computer model or othercomputerized representation of the object 112. A variety of arrangementsand techniques are known in the art to achieve controlled linearmovement along one or more axes. The x-y-z positioning assembly 108 may,for example, include a number of stepper motors 109 to independentlycontrol a position of the extruder 106 within the working volume alongeach of an x-axis, a y-axis, and a z-axis. More generally, the x-y-zpositioning assembly 108 may include without limitation variouscombinations of stepper motors, encoded DC motors, gears, belts,pulleys, worm gears, threads, and so forth. For example, in one aspectthe build platform 102 may be coupled to one or more threaded rods by athreaded nut so that the threaded rods can be rotated to provide z-axispositioning of the build platform 102 relative to the extruder 106. Thisarrangement may advantageously simplify design and improve accuracy bypermitting an x-y positioning mechanism for the extruder 106 to be fixedrelative to a build volume. Any such arrangement suitable forcontrollably positioning the extruder 106 within the working volume 114may be adapted to use with the printer 100 described herein.

In general, this may include moving the extruder 106, or moving thebuild platform 102, or some combination of these. Thus it will beappreciated that any reference to moving an extruder relative to a buildplatform, working volume, or object, is intended to include movement ofthe extruder or movement of the build platform, or both, unless a morespecific meaning is explicitly provided or otherwise clear from thecontext. Still more generally, while an x, y, z coordinate system servesas a convenient basis for positioning within three dimensions, any othercoordinate system or combination of coordinate systems may also orinstead be employed, such as a positional controller and assembly thatoperates according to cylindrical or spherical coordinates.

The controller 110 may be electrically or otherwise coupled in acommunicating relationship with the build platform 102, the x-y-zpositioning assembly 108, and the other various components of theprinter 100. In general, the controller 110 is operable to control thecomponents of the printer 100, such as the build platform 102, the x-y-zpositioning assembly 108, and any other components of the printer 100described herein to fabricate the object 112 from the build material.The controller 110 may include any combination of software and/orprocessing circuitry suitable for controlling the various components ofthe printer 100 described herein including without limitationmicroprocessors, microcontrollers, application-specific integratedcircuits, programmable gate arrays, and any other digital and/or analogcomponents, as well as combinations of the foregoing, along with inputsand outputs for transceiving control signals, drive signals, powersignals, sensor signals, and so forth. In one aspect, this may includecircuitry directly and physically associated with the printer 100 suchas an on-board processor. In another aspect, this may be a processorassociated with a personal computer or other computing device coupled tothe printer 100, e.g., through a wired or wireless connection.Similarly, various functions described herein may be allocated betweenan on-board processor for the printer 100 and a separate computer. Allsuch computing devices and environments are intended to fall within themeaning of the term “controller” or “processor” as used herein, unless adifferent meaning is explicitly provided or otherwise clear from thecontext.

A variety of additional sensors and other components may be usefullyincorporated into the printer 100 described above. These othercomponents are generically depicted as other hardware 134 in FIG. 1, forwhich the positioning and mechanical/electrical interconnections withother elements of the printer 100 will be readily understood andappreciated by one of ordinary skill in the art. The other hardware 134may include a temperature sensor positioned to sense a temperature ofthe surface of the build platform 102, the extruder 126, or any othersystem components. This may, for example, include a thermistor or thelike embedded within or attached below the surface of the build platform102. This may also or instead include an infrared detector or the likedirected at the surface 116 of the build platform 102.

In another aspect, the other hardware 134 may include a sensor to detecta presence of the object 112 at a predetermined location. This mayinclude an optical detector arranged in a beam-breaking configuration tosense the presence of the object 112 at a predetermined location. Thismay also or instead include an imaging device and image processingcircuitry to capture an image of the working volume and to analyze theimage to evaluate a position of the object 112. This sensor may be usedfor example to ensure that the object 112 is removed from the buildplatform 102 prior to beginning a new build on the working surface 116.Thus the sensor may be used to determine whether an object is presentthat should not be, or to detect when an object is absent. The feedbackfrom this sensor may be used by the controller 110 to issue processinginterrupts or otherwise control operation of the printer 100.

The other hardware 134 may also or instead include a heating element(instead of or in addition to the thermal element 130) to heat theworking volume such as a radiant heater or forced hot air heater tomaintain the object 112 at a fixed, elevated temperature throughout abuild, or the other hardware 134 may include a cooling element to coolthe working volume.

An extruder design of the printer 100 may use a printed circuit board(PCB) heating element that includes a through hole through which anextruder nozzle may pass. The PCB can be adhered to a metal plate thatabsorbs and transfers heat to the extruder nozzle. There may be one ormore PCB copper traces that may be electrically coupled to the metalplate. The PCB copper traces may be manufactured to a tolerance suchthat their resistance changes predictably with temperature. With thisknown relationship, a calibrated current through the copper traces canprovide a voltage indicative of the current temperature at the coppertraces, from which other temperatures (metal plate, extruder nozzle) canbe reliably inferred.

FIG. 2 shows a combined heater and temperature sensor integrated with aprinted circuit board (PCB). As shown, an extrusion tool head 200 for athree-dimensional printer may generally include an extrusion nozzle 202,drive components 204 to drive a build material into and through theextrusion nozzle 202, and a PCB 206. The PCB 206 may include a hole 212through which the extrusion nozzle 202 can pass, which may be filledafter assembly with any suitable potting material or other thermal orelectric insulator or conductor as desired. The PCB 206 may include aheating element 214 such as a resistive heating element that surroundsor is otherwise placed in close proximity to, and more specifically inthermal contact with, the extrusion nozzle 202 in order to create a hotzone to melt a build material in a chamber coupled to the extrusionnozzle 202 in order to extrude the build material through the extrusionnozzle 202. It will be appreciated that thermal contact may be achievedby direct physical contact or by contact through any suitable thermallyconducting material(s).

The conductive traces 208 that may be formed of any suitably conductivematerial such as copper, aluminum, or the like. The conductive traces208 may assume any suitable geometry within a plane of the PCB 206 suchas spiral pattern or a series of adjacent linear runs. Where the PCB 206has two or more layers, the conductive traces 208 may be on one or moresuch layers. In general, the use of longer, thinner traces providesgreater resistance per unit of length and correspondingly more sensitivemeasurements, however no particular geometry or dimensions are required,provided that the relationship between temperature and resistance can beaccurately characterized.

The heating element 214 may be electrically coupled to and driventhrough one or more conductive traces 208 on the PCB 206 that aremanufactured to have a resistance that changes predictably withtemperature. By applying a calibrated current to these conductive traces208 and measuring the resulting voltage, the temperature of the traces(and by inference, the extrusion nozzle 202) can be determined. Eachconductive trace 208 may have a first end 216 electrically coupled tothe heating element 214 through a contact or the like, and have apredetermined relationship of resistance to temperature. Each conductivetrace 208 may have a second end 218 electrically coupled to the powersupply 210 through one or more wires. In general the heating element 214may include one or more discrete heating element components coupled toor integrated into the PCB 206, such as resistive heating elements orthe like. In another aspect, the heating element 214 may be a resistiveheating element formed of a length of resistive material. This mayadvantageously be formed of a length of the conductive trace 208,eliminating the need for a separate, discrete heater.

Processing circuitry 220 may be coupled to the power supply 210 tocontrol operation of the PCB 206, and more particularly to drive aheating circuit including the conductive traces 208 and the heatingelement 214 alternately in a heating mode and a temperature sensing modeas generally described herein. The processing circuitry 220 may also becoupled to a voltage sensing circuit 222 that provides a voltagedifferential across the conductive traces 208 or some portion thereof.It will be understood that while voltage sensing is depicted across theoutput of the power supply, voltage sensing may as a practical matteroccur in a number of places. For example, voltage sensing may beperformed across a single trace on the PCB 206 from a contact for thepower supply 210 to a contact for the heating element 214. In anotheraspect the voltage sensing may be performed across the entire powercircuit (e.g., from a positive to a negative contact of the powersupply); however in this case, a load from the heating element might beindependently measured, particularly where the load is known to benon-temperature sensitive, and calibrated out of a voltage sensingmeasurement across the conductive traces 208. In another aspect, thecontrol circuitry 220 may selectively bypass the heating element 214 orotherwise isolate the lengths of conductive trace with a relay, switchor other low resistance coupling when in a temperature sensing mode inorder to isolate a resistance measurement across the conductive traces208, and then remove the bypass when returning to a heating mode. Moregenerally, a variety of techniques may be used to isolate a voltage dropacross some or all of the conductive traces 208 in order to measureresistance and calculate temperature thereof based upon the known,predetermined relationship between temperature and resistance for theconductive traces 208.

While FIG. 2 shows the PCB through hole approximately in the center ofthe PCB 206, it should be understood that the hole may be located at anylocation on the PCB 206 that allows for the placement of the extrusiontool head 200 components.

In this configuration, the traces 208 may be driven from a power supply210 in two alternating modes. In one mode, high-current may be appliedby the power supply 210 to heat the heating element 214. In a secondmode, a calibrated, low-current signal may be applied by the powersupply 210 to the traces 208 to determine the temperature of the heatingelement or the extrusion nozzle 202. In the second mode, the temperaturemay be determined by applying the calibrated current to the trace 208,measuring the voltage on the trace 208 that results from the calibratedcurrent, and comparing the measured voltage to temperature data that iscalibrated to the resistance of the traces 208. Additionally, there maybe temperature data that relates the temperature or resistance of thetraces 208 to the temperature of the heating element or extrusion nozzle202. Therefore, once the resistance and temperature of the traces 208 isknown, the temperature of the heating element or extruder nozzle may bedetermined.

In a non-limiting example of the trace and heating element configurationfor temperature determination, two traces 208 may be connected in serieswith the heating element with a first trace 208 connected between thepower supply 210 and a first heating element contact and a second trace208 connected between a second heating element contact and the powersupply 210. During the second mode of operation, while the calibratedcurrent is applied, a first voltage across the two traces 208 andheating element may be determined as discussed above. Additionally, asecond voltage may be measured across the first heating element contactand the second heating element contact to determine the voltage acrossthe heating element. Then the second voltage can be subtracted from thefirst voltage to determine the voltage across only the traces 208. Asstated above, once the voltage is determined for the traces 208, thetemperature of the traces and heating element may be determined.

The high-current mode (or “heating mode”) and the low-current mode (or“sensing mode”) may usefully operate over a shared circuit to both heatthe extrusion nozzle 202 and determine its temperature. In anotheraspect, the high-current mode and the low-current mode may be operatedover parallel circuits—one coupled to the heating element 214 and onecoupled to a conductive trace 208. Switching between modes may beperformed periodically at any regular, varying, or random interval. Ingeneral, this approach advantageously reduces the number of wires andcomponents required for concurrent temperature sensing and heating.

For meltable plastics such as PLA or ABS used in common extrusion-basedthree-dimensional printing, the power supply 210 may apply sufficientcurrent to heat the extrusion nozzle 202 to at least one hundred degreesCentigrade. The amount of current required to achieve this temperaturewithin the extruder may vary according to components used and theconfiguration of the physical arrangement of the heating element(s).Further, the desired operating temperature range may vary according tothe build materials used in the extrusion process.

In the low-current mode, the processing circuitry 220 may control thepower supply 210 to apply a calibrated current to the conductive traces208. As described above, the processing circuitry 220 may be furtherconfigured to measure the voltage resulting from the applied currentand, using Ohm's law and the predetermined relationship betweentemperature and resistance for the conductive traces 208, to calculate atemperature of the conductive traces 208. With this information, thetemperature of the extrusion nozzle 202 may be inferred, or calculateddirectly from the measure voltage using a suitable mathematical model.

The processing circuitry 220 may also determine whether, based on acalculated temperature and a predetermined target temperature,additional heating is required, and the processing circuitry 220 maycontrol the system in the high-current mode accordingly to move thecalculated temperature for a subsequent measurement toward the targettemperature.

FIG. 3 shows a method for operating a printed circuit board withintegrated temperature sensing as described above.

The method 300 may begin with providing an assembly including theprinted circuit board as shown in step 302. In general, the assembly mayinclude the printed circuit board, an extrusion nozzle passing through ahole in the printed circuit board, a heating element mounted to theprinted circuit board and thermally coupled to the extrusion nozzle, anda conductive trace on the printed circuit electrically coupled to and inseries with the heating element, all as generally described above. Inother embodiments, the conductive trace may be coupled in parallel withthe heating element or otherwise arranged in a suitable electroniccircuit on the printed circuit board with the power supply, heatingelement, voltage sensing circuitry, and processing circuitry. Asdescribed in the various embodiments above, the conductive trace usedfor measuring voltage may form a single length of trace, such as from apower supply terminal to a heating element terminal, or the conductivetrace may include multiple segments completing a circuit between thepositive and negative terminals of a power supply, such as by includinga first lead from a first contact of the heating element and a secondlead from a second contact of the heating element. More generally, anysuitable circuit may be used provided that the trace has a knownrelationship between temperature and resistance. The conductive tracemay be formed of copper, aluminum or any other suitable metal or otherconductive material(s).

As shown in step 304, a relationship may be determined of thetemperature to resistance for the conductive trace. While illustrated asoccurring after the assembly is provided, it will be appreciated thatthis step may be performed at any time prior to calculating atemperature. For example, the relationship may be determined when theprinted circuit board is fabricated, or after assembly into an extrusionsystem. In another aspect, the relationship may be measured using anonboard calibration circuit immediately prior to use. Howeverdetermined, the relationship may be substituted into Ohm's law to permitcalculation of temperature as a function of a known current and ameasured voltage across the conductive trace.

As shown in step 306, the heating element may be powered through theconductive trace (from a power supply or the like) in a high-current orheating mode to heat the heating element.

As shown in step 308, the heating element may be powered through theconductive trace in a low-current or sensing mode with a known currentand a voltage across the conductive trace may be measured. As notedabove, the resistance of the heating element may be accounted for(either as a fixed or temperature-varying quantity), or the voltage maybe measured only across the conductive trace. Accordingly, in oneembodiment, the method may include determining a second voltage across afirst contact and a second contact of the heating element andsubtracting the second voltage from the voltage across a length of theconductive trace that includes two segments in series with the twoterminals of the heating element. In other embodiments, the conductivetrace may form an independent circuit in parallel with the heatingelement, and may be electrically isolated from or coupled to the powersupply according to the desired mode. More generally, any technique formeasuring voltage along a length of conductive trace that has a knownrelationship of temperature to resistance may be usefully employed in atemperature sensing measurement as contemplated herein.

As shown in step 310, the method 300 may include determining atemperature of the conductive trace based upon the voltage and theknown, predetermined relationship between resistance and temperature forthe conductive trace.

As shown in step 312, the method may include calculating a temperatureof the extrusion nozzle based upon the temperature of the conductivetrace. The relationship between the temperature of the conductive traceand the temperature of the extrusion nozzle may be empiricallydetermined or estimated using physical modeling or the like based uponthe structure of the extrusion nozzle, heater, circuit board, and soforth. It will be appreciated that, while illustrated as separate steps,the extrusion nozzle temperature may be calculated directly from thesensed voltage across the conductive trace using a suitably adaptedmathematical model.

As shown in step 314, a control loop may be implemented by determiningwhether the temperature of the extrusion nozzle has reached apredetermined target value. If the temperature is at or above thetarget, then the method 300 may return to step 308 where the temperaturemay again be sensed. If the temperature is below the target, then themethod 300 may return to step 306 where the heating element may beheated. The duration of heating in step 306 may be fixed, or may varyaccording to, e.g., a magnitude of the difference between the targettemperature and the calculated temperature for the extrusion nozzle.

FIG. 4 shows a method for fabricating conductive traces on a printedcircuit board. In the above techniques, it is generally advantageous tohave conductive traces with known resistance/temperaturecharacteristics. While the shape and/or amount of copper in the tracesmay be calculated for a desired temperature/resistance relationshipbased on physical properties of the copper, it may be impractical tomanufacture such traces within a desired tolerance. In particular, incurrent manufacturing techniques the width of traces may varysignificantly (e.g., 10-15%) in a manner that introduces excessvariability into resulting resistance, thus making width a poormanufacturing parameter for controlling resistance; however, the heightof a layer may be usefully controlled during fabrication to obtaincalibrated traces notwithstanding variable width. These and similartechniques are described below for fabricating circuit boards withtraces having temperature/resistance characteristics meeting desiredspecifications.

As shown in step 402, the method 400 may begin with fabricating aprinted circuit board including a through-hole for an extrusion nozzleand a mounting location adjacent to the through-hole shaped for aheating element. The printed circuit board may be fabricated using anysuitable techniques, the variety of which are well known to those ofordinary skill in the art, and may include one layer, two layer, orother multi-layer circuit board fabrication techniques.

As shown in step 404, the method 400 may include adding a copper traceto the printed circuit board extending from a contact of the mountinglocation (for the heating element) to a contact for a power supply,which would typically be off the printed circuit board for high-powerheating applications, but is not necessarily so.

As shown in step 406, the method 400 may include measuring a resistanceof the copper trace using any measurement circuitry amenable to use in aPCB fabrication environment.

As shown in step 308, the method 400 may include modifying the coppertrace to adjust the resistance toward a predetermined resistance. Avariety of techniques may be used to make such modifications. In oneaspect, this may include layering additional copper onto a pattern ofthe copper trace in order to decrease resistance per unit length. Byclosely controlling the amount of copper added, the increased thicknessand resulting change in resistance may be accurately estimated. In oneaspect, this may include maintaining a substantially constanttemperature—that is, a temperature that will not change in a manner thataffects the resistance measurement or the resulting resistance per unitlength, either within measurement limits of the testing circuitry ordesign limits of the resulting conductive trace—while layeringadditional copper. Similarly, the temperature may be varied within somerange such as an intended operating range over which linear behavior isdesired. By concurrently modifying the copper trace and measuring theresistance, suitable results may be achieved in a single, continuousfabrication step.

Other techniques may also or instead be employed. For example, modifyingthe copper trace may include cutting the copper trace to a lengthcorresponding to the predetermined resistance. A suitable length forcutting may be determined, e.g., based on the aggregate resistance (asmeasured) and known length of the copper trace. In another aspect, thecopper trace may include a number of traces having, e.g., differentlengths or thicknesses, and modifying the copper trace may includeselectively coupling one or more of the plurality of traces having anaggregate resistance closest to the predetermined resistance to thecontact of the mounting location and the contact for the power supply.The traces may, e.g., be connected in series, in parallel, or in anycombination of these to obtain a desired lump resistance parameter at aspecific temperature.

As shown in step 410, after modifications the resistance of the coppertrace may be measured again.

As shown in step 412, the measured resistance may be compared to atarget resistance. While the relationship of resistance to temperaturemay be estimated or measured, this step may be simplified by comparing asingle measurement at a single temperature to a discrete target. Oncethe scalar target is achieved, a more complete characterization may beperformed as desired for accuracy of performance. If the measuredresistance matches the target resistance within some predeterminedtolerance, then the method 400 may proceed to step 414. If the measuredresistance is outside the predetermined tolerance, then the method 400may return to step 408 where the copper trace is once again modified tobring the actual resistance closer to the target resistance.

As shown in step 414, any number of finishing steps may be performed.This may for example include assembling components on the printedcircuit board for use as intended. This may also include measuring orotherwise characterizing a temperature/resistance relationship over somerange (such as an intended operating range for the finished product),and encoding the relationship into firmware or the like on the printedcircuit board to support subsequent calibrated operation of the finishedproduct. More generally, any additional steps for accurately capturingthe temperature/resistance relationship of the copper traces, using thetemperature sensing capabilities of the finished product, or otherwiseshipping and deploying the finished product may be performed.

FIG. 5 shows a heating element formed of a conductive trace. As notedabove, the heating element may advantageously be formed from the sameconductive trace used to measure temperature. As shown in FIG. 5, thisheating element 500 may be formed of a material such as copper on aprinted circuit board. While depicted as an octagonal spiral, anysuitable geometry may be employed. In general, a first end 502 may becoupled to a current source and a second end 504 may be coupled to aground (or vice versa). The second end 504 may terminate in an openingfor an extrusion nozzle to pass through. The second end 504 may alsoinclude a via to another layer of the printed circuit board for a returnpath to the power source. A similar spiral shape may also be provided inone or more other layers of the printed circuit board (not shown)including the other layer that provides the return path. Thisarrangement advantageously removes the need for a separate, discreteheating element and permits the conductive trace to serve as both atemperature sensing circuit and a heating circuit on the same printedcircuit board.

The methods or processes described above, and steps thereof, may berealized in hardware, software, or any combination of these suitable fora particular application. The hardware may include a general-purposecomputer and/or dedicated computing device. The processes may berealized in one or more microprocessors, microcontrollers, embeddedmicrocontrollers, programmable digital signal processors, or otherprogrammable device, along with internal and/or external memory. Theprocesses may also, or instead, be embodied in an application specificintegrated circuit, a programmable gate array, programmable array logic,or any other device or combination of devices that may be configured toprocess electronic signals. It will further be appreciated that one ormore of the processes may be realized as computer executable codecreated using a structured programming language such as C, an objectoriented programming language such as C++, or any other high-level orlow-level programming language (including assembly languages, hardwaredescription languages, and database programming languages andtechnologies) that may be stored, compiled or interpreted to run on oneof the above devices, as well as heterogeneous combinations ofprocessors, processor architectures, or combinations of differenthardware and software.

Thus, in one aspect, each method described above and combinationsthereof may be embodied in computer executable code that, when executingon one or more computing devices, performs the steps thereof. In anotheraspect, the methods may be embodied in systems that perform the stepsthereof, and may be distributed across devices in a number of ways, orall of the functionality may be integrated into a dedicated, standalonedevice or other hardware. In another aspect, means for performing thesteps associated with the processes described above may include any ofthe hardware and/or software described above. All such permutations andcombinations are intended to fall within the scope of the presentdisclosure.

It should further be appreciated that the methods above are provided byway of example. Absent an explicit indication to the contrary, thedisclosed steps may be modified, supplemented, omitted, and/orre-ordered without departing from the scope of this disclosure.

The method steps of the invention(s) described herein are intended toinclude any suitable method of causing such method steps to beperformed, consistent with the patentability of the following claims,unless a different meaning is expressly provided or otherwise clear fromthe context. So for example performing the step of X includes anysuitable method for causing another party such as a remote user or aremote processing resource (e.g., a server or cloud computer) to performthe step of X. Similarly, performing steps X, Y and Z may include anymethod of directing or controlling any combination of such otherindividuals or resources to perform steps X, Y and Z to obtain thebenefit of such steps.

While particular embodiments of the present invention have been shownand described, it will be apparent to those skilled in the art thatvarious changes and modifications in form and details may be madetherein without departing from the spirit and scope of this disclosureand are intended to form a part of the invention as defined by thefollowing claims, which are to be interpreted in the broadest senseallowable by law.

What is claimed is:
 1. A device comprising: a printed circuit board; ahole in the printed circuit board; an extrusion nozzle passing throughthe hole; a heating element on the printed circuit board, the heatingelement positioned in thermal contact with the extrusion nozzle; and aconductive trace on the printed circuit board, the conductive tracehaving a first end coupled to a contact of the heating element, theconductive trace having a predetermined relationship of resistance totemperature.
 2. The device of claim 1 wherein the conductive trace is acopper trace.
 3. The device of claim 1 further comprising a secondconductive trace on the printed circuit board electrically coupled to asecond contact of the heating element.
 4. The device of claim 1 furthercomprising a power supply electrically coupled to a second end of theconductive trace.
 5. The device of claim 4 wherein the power supplyoperates in a first mode where high current is applied to the heatingelement to create heat in the heating element.
 6. The device of claim 5wherein the power supply operates in a second mode where a calibratedcurrent is applied to the heating element and a voltage across theconductive trace is measured, thereby permitting a determination of theresistance of the conductive trace and, based upon the predeterminedrelationship of resistance to temperature, the temperature of theconductive trace.
 7. The device of claim 1 further comprising processingcircuitry configured to operate the power supply in a first mode wherehigh current is applied to the heating element to create heat in theheating element.
 8. The device of claim 7 wherein the power supply heatsthe heating element to at least one hundred degrees Centigrade.
 9. Thedevice of claim 7 wherein the processing circuitry is further configuredto operate the power supply in a second mode where a calibrated currentis applied to the heating element, the processing circuitry furtherconfigured to measure a voltage across the conductive trace.
 10. Thedevice of claim 9 wherein the processing circuitry is configured tocalculate a temperature of the extrusion nozzle based upon the voltage.11. The device of claim 1 wherein the heating element is a resistiveelement formed by a length of the conductive trace.
 12. A methodcomprising: providing an assembly including a printed circuit board, anextrusion nozzle passing through a hole in the printed circuit board, aheating element mounted to the printed circuit board and thermallycoupled to the extrusion nozzle, and a conductive trace on the printedcircuit board electrically coupled to and in series with the heatingelement; determining a relationship of temperature to resistance for theconductive trace; powering the heating element through the conductivetrace in a first mode to heat the heating element; powering the heatingelement through a conductive trace in a second mode with a known currentand measuring a voltage across the conductive trace; and determining atemperature of the conductive trace based upon the voltage.
 13. Themethod of claim 12 further comprising calculating a temperature of theextrusion nozzle based upon the temperature of the conductive trace. 14.The method of claim 12 wherein the conductive trace includes a firstlead from a first contact of the heating element and a second lead froma second contact of the heating element.
 15. The method of claim 14further comprising determining a second voltage across the first contactand the second contact of the heating element and subtracting the secondvoltage from the voltage across the conductive trace.
 16. The method ofclaim 12 wherein the conductive trace includes a copper trace.
 17. Amethod comprising: fabricating a printed circuit board including athrough-hole for an extrusion nozzle and a mounting location adjacent tothe through-hole shaped for a heating element; adding a copper trace tothe printed circuit board from a contact of the mounting location to acontact for a power supply; measuring a resistance of the copper trace;and modifying the copper trace to adjust the resistance toward apredetermined resistance.
 18. The method of claim 17 wherein modifyingthe copper trace includes layering additional copper onto a pattern ofthe copper trace.
 19. The method of claim 18 wherein modifying thecopper trace includes maintaining a substantially constant temperatureof the copper while layering additional copper and concurrentlymeasuring the resistance.
 20. The method of claim 17 wherein modifyingthe copper trace includes cutting the copper trace to a lengthcorresponding to the predetermined resistance.
 21. The method of claim17 wherein the copper trace includes a plurality of traces, and whereinmodifying the copper trace includes selectively coupling one or more ofthe plurality of traces having an aggregate resistance closest to thepredetermined resistance to the contact of the mounting location and thecontact for the power supply.